The overall aim of this project is to develop a genetic approach to analyze the nature and role of adenoviral gene products responsible for the striking differences observed in viral oncogenicity and cellular malignancy between the group A (type 12) viruses and the group C (type 5) human adenoviruses. Our specific objectives are: (1) To isolate and characterize conditional-lethal, host-range, transformation-defective mutants of type 12. (2) To characterize the transformation phenotype of these mutants in cells derived from inbred mice. (3) To establish an inbred mouse host system to assess oncogenic capacity of the mutants, and the malignancy of the cells transformed by them, and in this way map the viral gene(s) responsible for induction of neoplasia by this virus.